Following the launch of MSN Weather on the Xbox One, the next Universal App we get to see from Microsoft could well be the long-awaited update to Groove Music. We know it's coming, we know it's going to support background audio, but as yet we've not seen anything from it.
In the same way as MSN Weather and Netflix just recently appeared in "Ready to Install," right now preview members using the latest build will also see Groove Music added to that list.
You can go and view it in the Store but nothing else. It currently errors out when you try to install it, and there are no Xbox specific screenshots to look at. But it's confirmed to be the new app by the "Available on" section which shows the console alongside PC, phones and HoloLens.
Given the way MSN Weather appeared and then became officially available on the preview, perhaps Groove is next in line for an early test. We'll have to wait and see.